The present invention deals with a drive system for a motor vehicle having a front axle and a plurality of rear axles, which are driven or can be driven, consisting of a central differential driven from an engine change-speed gearbox unit, an inter-axle differential, following the central differential in the direction of the power flow, between the front axle and a first, front, rear axle, and a drive for at least one further rear axle, and axle differentials in each of the axles.
Such drive systems having only one front axle and two rear axles in tandem arrangement are used, for instance, in trucks, and such drive systems having three rear axles are used in trucks for loads whose center of gravity lies very far to the rear. In all of these drive systems, an optimum distribution of the drive torques to the driven axles is aimed at. Since the wheel base between the two unsteered rear axles, which are present in any case, has to be kept very short, it is not possible to attach a central or inter-axle differential between these two axles in order to achieve a balanced torque distribution.
U.S. Pat. No. 4,977,972 discloses a system of the generic type in which the central differential is also arranged constructionally in front of the first rear axle and has three outputs, one each for the front axle and for the first rear axle and one for two further rear axles. The output for the second and third rear axles is passed through the casing of the axle differential of the first rear axle, but without being connected there.
A disadvantage with this arrangement is that the central differential, which is voluminous per se, comes to lie relatively far forward in the chassis of the vehicle, a factor which, given the length of a conventional engine gearbox unit, is very obstructive and completely rules out the design as a forward-control-type truck with center engine. It also requires a large number of very short universal-joint shafts, which must be especially short between central differential and first rear axle in order to be able to accommodate the central differential behind the engine gearbox unit. This increases costs and wear. In addition, the central differential arranged far forward has an adverse effect on the weight distribution of the unladen vehicle.
It is a principle object of the present invention to provide a drive system which avoids the foregoing disadvantages. The drive system is to have as short and as inexpensive a construction as possible and as few units and connecting shafts as possible.